Disable prev/next buttons for contain

I'm wondering if you have any suggestions for determining if you've arrived at the boundary of the carousel when the contain option is specified. (So that one could say for instance disable the next or previous buttons).

When not using the indicator dots for position feedback this kind of behavior _appears_ confusing, though I understand the logic here.

Example:


Start by reviewing Flickity's contain option and the existing prev/next button behavior. Determine how the carousel exposes arrival at either boundary, then define disabled-button behavior for contained carousels and verify it without relying on indicator dots.

Written by the indexing model from the issue text.